Methods and apparatus for charging a battery in a peripheral device

ABSTRACT

A power manager for managing power delivered to a battery operated peripheral device is disclosed. The power manager includes an input current limiter arranged to suppress a power surge associated with an insertion event by a power cable arranged to provide an external voltage. A voltage converter unit coupled to the input current limiter converts the received external voltage to a supply voltage that is transmitted by way of a main bus to a voltage sensor unit coupled thereto. During the insertion event, a comparator unit coupled to the voltage sensor, sends a first switching signal to a switchover circuit that responds by connecting the peripheral device and an uncharged battery to the main bus such that the supply voltage is provided thereto. When the battery is substantially fully charged, the switchover circuit responds by electrically disconnecting the battery so as to not overcharge the battery.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/270,901 (Attorney Docket APL1P224C1) entitled “METHODS AND APPARATUSFOR CHARGING A BATTERY IN A PERIPHERAL DEVICE,” filed Nov. 10, 2005,which is a continuation of U.S. patent application Ser. No. 10/278,752(Attorney Docket APL1P224) entitled “METHODS AND APPARATUS FOR CHARGINGA BATTERY IN A PERIPHERAL DEVICE” filed Oct. 22, 2002 and which issuedas U.S. Pat. No. 6,995,963 on Feb. 27, 2006, which are incorporatedherein by reference, and which, in turn, claim the benefit of priorityunder 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No.60/345,253, entitled “METHODS AND APPARATUS FOR CHARGING A BATTERY IN APERIPHERAL DEVICE VIA A FIREWIRE CABLE” filed on Oct. 22, 2001, which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates generally to computing systems. Specifically, amethod and apparatus for managing power delivered by way of a FireWirecable to a battery operated peripheral device.

2. Description of Related Art

FireWire is an IEEE1394 compliant High Performance Serial Bus thatprovides two types of data transfer: asynchronous and isochronous.Asynchronous is for traditional load-and-store applications where datatransfer can be initiated and an application interrupted as a givenlength of data arrives in a buffer. Isochronous data transfer ensuresthat data flows at a pre-set rate so that an application can handle itin a timed way while providing the bandwidth needed for audio, imaging,video, and other streaming data. Isochronous service means it guaranteeslatency or the length of time between a requested action and when theresulting action occurs which is a critical feature in supporting realtime video, for example. FireWire provides a high-speed serial bus withdata transfer rates of 100, 200, or 400 Mbps as well as a singleplug-and-socket connection on which up to 63 devices can be attachedwith data transfer speeds up to 400 Mbps (megabits per second). In thisway, FireWire offers a standard, simple connection to all types ofconsumer electronics, including digital audio devices, digital VCRs anddigital video cameras; as well as to traditional computer peripheralssuch as optical drives and hard disk drives.

The standard FireWire cable consists of six wires in which data is sentvia two separately-shielded twisted pair transmission lines that arecrossed in each cable assembly to create a transmit-receive connection.Two more wires carry power (8 to 28 v, 1.5 A max.) to remote devices. Insome cases, such as with DV camcorders manufactured by the SonyCorporation of Japan, a 4 conductor FireWire cable is used (configuredas the 6 wire cable but without the power wires) that terminate insmaller, 4 prong connectors. To connect a four prong device, such as theSony DV camcorder with a standard IEE1394 FireWire device or interfacecard, an adapter cable is required having 4 prongs on one side and 6 onthe other. In this way, the data lines are connected while omitting thepower connection.

In those situations, however, when a battery operated six prongperipheral device is coupled to a FireWire cable, it is important forthe power delivered to the device (typically 1.8 v, 3.3, or 5.0 v) to beboth stable and reliable especially when the FireWire cable is eitherconnected or disconnected.

Therefore, what is required is a method and apparatus for managing powerdelivered by way of a FireWire cable to a battery operated peripheraldevice.

SUMMARY OF THE INVENTION

According to the present invention, methods, apparatus, and systems aredisclosed for managing power in a battery powered portable device isdisclosed.

In one embodiment, an apparatus is described that includes at least acircuit, a battery, a port that includes a power line and serial dataline, and a power management unit, coupled to the circuit, the battery,and the port. In the described embodiment, the power management unitcontains instructions that when executed by the power management unit:(i) powers the circuit with the battery if the power line does notprovide power; and (ii) powers the circuit and charges the battery withpower provided by the power line if the power line provides power to theapparatus.

In another embodiment, a method for providing power to a circuitcontained within a portable device from either a battery contained inthe device or an external power source when plugged into a portconfigured to receive both power and data at the device, the method iscarried out by performing at least the following operations.Ascertaining if the external power source is plugged into the port ofthe device, and either: providing power to the circuit from the batterywhen the external power source is not plugged into the device, orproviding power from the external power source to the circuit and thebattery used to at least recharge the battery when the external powersource is plugged into the device and when the output of the battery isbelow a supply voltage by more than a threshold, or providing power fromthe external power source only to the circuit when the external powersource is plugged into the device and the output of the battery iswithin the threshold of the supply voltage.

In still another embodiment, a battery powered device is described thatincludes at least a rechargeable battery, a serial port that interfaceswith a serial bus cable for transmitting data to or from the device thatincludes a plurality of data pins and at least a power pin, a voltagesensor that senses a voltage on the power pin, and a battery chargingcircuit that draws a charging current through the power pin of theserial port to charge the battery when the battery is substantiallyuncharged.

In still another embodiment, a method for charging a battery of aperipheral device, is described. The method is carried out by performingat least the following operations: inserting a serial bus cable into aserial port of the peripheral device, the serial port comprising a powerpin and a plurality of data pins through which data can be transmittedto or from the peripheral device, sensing that the voltage at the powerpin of the serial port is above a selected threshold, and drawing acharge current through the power pin of the serial port to charge thebattery of the peripheral device.

Another embodiment describes a system that includes a battery powereddevice having a rechargeable battery and a battery charging circuit, anda serial bus cable coupled to the battery powered device where theserial bus cable includes at least a power transmission line and aplurality of data transmission lines and can transmit data to or fromthe battery powered device over the data transmission lines. The batterycharging circuit of the battery powered device draws a charging currentthrough the power transmission line of the serial bus cable if therechargeable battery is not fully charged.

A method for managing power delivered to a battery-operated peripheraldevice by way of a cable that includes a number of lines at least one ofwhich is a power line arranged to carry electrical power from anelectrical supply to the device is also described. The method includesat least the following operations: detecting a status for the device,wherein the status is based on whether a first condition relating to abattery in the device has occurred and whether a second conditionrelating to connection of the cable to the electrical supply hasoccurred, drawing electrical power from the electrical supply at a firstcurrent if the device has a first status, and drawing electrical powerfrom the electrical supply at a second current level if the device has asecond status.

A portable consumer electronic product includes a sensor unit arrangedto detect a status for the device, wherein the status is based onwhether a first condition relating to a battery in the device hasoccurred and whether a second condition relating to connection of thecable to the electrical supply has occurred, and a switchover circuitarranged to draw electrical power from the electrical supply at a firstcurrent if the device has a first status, and to draw electrical powerfrom the electrical supply at a second current level if the device has asecond status.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1A shows a power manager unit with a fully discharged batterycoupled to an active FireWire cable in accordance with an embodiment ofthe invention.

FIG. 1B shows the power manager unit of FIG. 1A where the battery isfully charged in accordance with an embodiment of the invention.

FIG. 1C shows the power manager unit of FIG. 1B where the FireWire cableof the invention.

FIG. 3 shows an exemplary response waveforms for the switchover statewhere the battery is fully charged.

FIGS. 4 and 5 show exemplary response waveforms for the switchover statewhere the battery is full and the Fire Wire is unplugged in two separatescenarios.

FIG. 6 shows an exemplary response waveforms for the switchover statewhere the battery is low and the FireWire is plugged.

FIG. 7 shows an exemplary response waveforms for the switchover statewhere the battery is low and the FireWire is unplugged.

FIG. 8 shows an exemplary response waveforms for the switchover statewhere the battery is empty and the FireWire is plugged.

FIG. 9 shows an exemplary response waveforms for the switchover statewhere the battery is empty and the FireWire is unplugged.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

Reference will now be made in detail to a preferred embodiment of theinvention. An example of the preferred embodiment is illustrated in theaccompanying drawings. While the invention will be described inconjunction with a preferred embodiment, it will be understood that itis not intended to limit the invention to one preferred embodiment. Tothe contrary, it is intended to cover alternatives, modifications, andequivalents as may be included within the spirit and scope of theinvention as defined by the appended claims.

In a battery powered FireWire compatible device, a method and apparatusfor supplying power to the device that can be used to either operate thedevice of charge the device's battery are described. In one embodiment,various power signals on a FireWire data bus coupled to the device,provide for operating the device and/or charging the device's internalbattery over a prescribed range of supply voltages. In a particularembodiment, the apparatus includes a built in surge suppression unit aswell as a FireWire power/battery switchover unit to ensure that a stableand reliable power supply is provided the device. In this way,additional power connectors are substantially eliminated thereby savingproduct cost and reducing product size.

The invention will now be described in terms a FireWire peripheral powermanagement unit suitable for supplying power to any FireWire compatibledevice. Such devices include, for example, personal digital assistants,personal MP3 player/recorders, and the like.

Accordingly, FIG. 1A shows a power manager unit 100 with a fullydischarged battery coupled to an active FireWire cable in accordancewith an embodiment of the invention. The power manager unit 100 includesan input current limiter 102 for suppressing a power surge caused by aFireWire cable insertion event related to voltage transients (i.e.,ground bounce) associated with an insertion of a powered FireWire cable104 to an input port 106. It should be noted, that this phenomenon isonly applicable to those peripheral devices capable of receiving aFireWire cable having a power wire included therein (such as a six prongtype FireWire cable). The input current limiter 102 is, in turn, coupledto a voltage converter unit 108 having an output 108′ arranged toconvert a received external voltage V_(ext) (in the form of a FireWirevoltage V_(FW) having a range of between 8 volts and 28 volts providedby the FireWire cable 104) to a supply voltage V_(cc) provided to a mainbus 110. Typically, the supply voltage V_(cc) can be approximately 1.8volts, approximately 3.3 volts, or approximately 5.0 volts each of whichis suitable for driving an active circuit 112 included in a batteryoperated peripheral device 113.

In the described embodiment, the voltage converter unit 108 is coupledto a voltage sensor 114 arranged to provide a voltage signal V_(sig) toa comparator unit 116. The comparator unit 116, based upon the voltagesignal V_(sig), provides a switchover signal V_(switch) to a switchovercircuit 118. In those cases where the voltage signal V_(sig) is above avoltage threshold V_(th) (indicative of a FireWire insertion eventhaving had occurred at the input port 106), the comparator unit 116provides a first switchover signal V_(switch1) to the switchover circuit118. The switchover circuit 118, in turn, responds to the firstswitchover signal V_(switch1) by connecting the main bus 110 to theactive circuit 112 (and thereby the supply voltage V_(cc)) and to abattery 120 when the battery 120 is substantially uncharged so as toprovide a charging current to the battery 120. As shown in FIG. 1B, inthose cases where the battery 120 is substantially fully charged, thecomparator circuit 116 sends a second switchover signal V_(switch2) thatcauses the switchover circuit 118 to disconnect the battery 120 from themain bus 110 so as to avoid overcharging the battery 120.

In those situations shown in FIG. 1C where the powered FireWire cable104 has been disconnected from the port 106, the voltage signal V_(sig)is below the voltage threshold V_(th) to which the comparator circuit116 responds by providing a third switchover signal V_(switch3) to theswitchover circuit 118. The switchover circuit 118 responds to the thirdswitchover signal V_(switch3) by disconnecting the main bus 110 from theactive circuit 112 and connecting the battery 120 in such a manner as toprovide a substantially uninterrupted supply voltage V_(cc) to theactive circuit 112.

Referring to FIG. 2, the switchover circuit 118 includes a comparator202 that helps to ensure a smooth transition from battery to FireWirepower and vice versa. The switch over circuit 118 ensures that thevoltage on the main supply bus 110 (VCC_MAIN) doesn't drop below apre-determined minimum voltage V_(min) (at which point a reset signal istypically provided). Accordingly, the FireWire voltage converter 108switches in/out when the voltage on the main bus 110 (V_(cc) MAIN) hasrisen/dropped above/below V_(min).

FIG. 3 shows an exemplary response waveforms for the switchover statewhere the battery is full and the FireWire is plugged in. After theFireWire cable 104 is plugged into the port 106, the output of theFireWire voltage converter 108 reaches its destination voltage within 15ms. When the output of the FireWire voltage converter 108 reaches theswitch over threshold V_(switch), the comparator 202 disconnects batterypower from the main supply bus 110. For a short period of time, neitherthe battery 120 nor the FireWire voltage converter 108 supply power toVCC_MAIN 110 and the voltage on VCC_MAIN 110 will drop until either ofthe voltage sensor 114 starts conducting such that the voltage cannotdrop below the voltage V_(MIN). Eventually the voltage sensor 114 startsconducting, pulling the voltage on bus 110 up to a pre-set voltage dropV_(f) below the destination output voltage of the FireWire voltageconverter 108.

FIGS. 4 and 5 show an exemplary response waveforms for the switchoverstate where the battery is full and the FireWire is unplugged in twoseparate scenarios. Initially, the voltage V_(VCC) _(—) _(MAIN) is V_(f)below the voltage of the FireWire voltage converter 108. Due to thesystem load, the output voltage of the FireWire voltage converter 108 isgoing to drop rapidly as the voltage sensor 114 discharges into the mainsupply bus 110. When FireWire 106 is unplugged the voltage at the outputof the FireWire voltage converter 108 is going to drop rapidly until thevoltage sensor 114 starts conducting. At this point the voltage at theoutput of the FireWire voltage converter 108 may or may not have notdropped below the switch over threshold Vswitch. There will be twopossible scenarios:

In one scenario shown in FIG. 4, the comparator threshold has beencrossed in which case, the battery 120 has to make up for the voltageV_(f). In a second scenario shown in FIG. 5, the comparator thresholdhas not been crossed.

FIG. 6 shows an exemplary response waveforms for the switchover statewhere the battery is low and the FireWire is plugged. In the describedembodiment, the battery is considered empty when it's voltage dropsbelow 3.45V. For the purpose of this discussion only therefore, thebattery voltage is considered to be at 3.3V. If the battery voltagedrops below 3.45V the system is turned off and less than 2 mA are drawnfrom the battery. Therefore the voltage the main bus 110 isapproximately equal to the battery voltage V_(BAT)=3.3V. After theFireWire connector 104 is plugged into the port 106, output 108′increases. If output 108′ increases above V_(VCC) _(—) _(MAIN) of 3.3V,the voltage sensor 114 starts conducting. The battery will be back fedfrom then on, until output 108′ reaches the switch over threshold.

FIG. 7 shows an exemplary response waveforms for the switchover statewhere the battery is low and the FireWire is unplugged. Initially, thevoltage V_(VCC) _(—) _(MAIN) on the main bus 110 is V_(f) below thevoltage of the FireWire voltage converter 108 resulting in the output108′ dropping off rapidly. When output 108′ drops below the switch overthreshold V_(switch), voltage converter 108 is going to back feed intothe battery until output 108′ drops below a level where voltage sensor114 loses conduction. If the latter occurs, output 108′ is going to bedischarged much slower as it is disconnected from the rest of thesystem. It has to be noted that this particular scenario is very rare asthe battery voltage recovers within short periods of time to a levelthat is above the 3.45V system shut down threshold.

FIG. 8 shows an exemplary response waveforms for the switchover statewhere the battery is empty and the FireWire is plugged. When the batteryis empty, V_(VCC) _(—) _(MAIN) is initially approximately ground leveland the battery charger circuit is disabled. If output 108′ charges up,V_(VCC) _(—) _(MAIN) is approximately one diode forward voltage dropbelow output 108′. (It should be noted that a reset circuit keeps thesystem 100 in constant reset below voltages of 3.135V) thereby enablinga battery charger circuit. If battery charger circuit supply voltage hasexceeded the lockout voltage of 4.1V, battery back feeding is preventedbecause the battery 120 is disconnected from the system 100. The batterycharger is activated when it's supply voltage exceeds the under voltagelock out threshold of 4.1V. To enable the battery charger, the voltageat the output of the FireWire voltage converter 108 must be one forwarddiode drop above the lock out voltage of the battery charger. Therefore,output 108′ has to rise above approximately 4.6V to activate thecharger.

FIG. 9 shows an exemplary response waveforms for the switchover statewhere the battery is empty and the FireWire is unplugged. When thebattery is empty and FireWire 104 is unplugged, the system 100 will rununtil VCC_MAIN drops rapidly below reset threshold voltage V_(reset,TH).In reset, the battery disconnect circuitry disconnects the battery fromthe system 100 when the battery voltage drops below 3.1V to avoid deepdischarge of the battery using a low voltage disconnect circuitry.

Although only a few embodiments of the present invention have beendescribed, it should be understood that the present invention may beembodied in many other specific forms without departing from the spiritor the scope of the present invention. Therefore, the present examplesare to be considered as illustrative and not restrictive, and theinvention is not to be limited to the details given herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

While this invention has been described in terms of a preferredembodiment, there are alterations, permutations, and equivalents thatfall within the scope of this invention. It should also be noted thatthere are many alternative ways of implementing both the process andapparatus of the present invention. It is therefore intended that theinvention be interpreted as including all such alterations,permutations, and equivalents as fall within the true spirit and scopeof the present invention.

1. An apparatus comprising: a circuit; a battery; a port that includes apower line and serial data line; and a power management unit, coupled tothe circuit, the battery, and the port, wherein the power managementunit contains instructions that when executed by the power managementunit: (i) powers the circuit with the battery if the power line does notprovide power; (ii) powers the circuit and charges the battery withpower provided by the power line if the power line provides power to theapparatus.
 2. The apparatus of claim 1, wherein the power managementunit further comprises a voltage converter to convert an external powersource voltage to a supply voltage if the external power source voltageis received through the port and is provided to the circuit.
 3. Theapparatus of claim 2, wherein the voltage converter of the powermanagement unit is a step down converter configured to step down theexternal power supply voltage to the supply voltage.
 4. The apparatus ofclaim 2, wherein the power management unit further comprises a chargecurrent generator to generate a charge current to charge the battery ifthe external power supply voltage is received through the port and abattery power source voltage is below the supply voltage by a threshold.5. The apparatus of claim 4, wherein the power management circuitfurther comprises a comparator to compare the battery power sourcevoltage to the supply voltage.
 6. The apparatus of claim 5, wherein thecomparator generates a first signal if the battery power source voltageis within the threshold from the supply, the first signal provided to acharge control circuit.
 7. The apparatus of claim 6, wherein the firstsignal further causes the charge circuit to disconnect the externalpower supply voltage from the battery to prevent over-charging of thebattery.
 8. The apparatus of claim 5, wherein the comparator generates asecond signal if the battery power source voltage is below the thresholdof the supply voltage, the second signal causing a charge circuit togenerate a charge current to charge the battery when the external powersupply voltage is received through the port.
 9. The apparatus of claim2, wherein the supply voltage is one of the following voltages:approximately 1.8 volts, approximately 3.3 volts, approximately 5.0volts; or 5.0 volts or less.
 10. The apparatus of claim 1, wherein thepower management unit further comprises a switch circuit configured toprevent substantial interruptions in providing power to the circuit whenswitching from the external power supply voltage to the battery powersource voltage or vice versa.
 11. The apparatus of claim 1, wherein theport is configured to receive at least one power line.
 12. The apparatusof claim 1, wherein the port is configured to receive at least one dataline arranged to form a transmit-and-receive connection with theexternal source.
 13. A method for providing power to a circuit containedwithin a portable device from either a battery contained in the deviceor an external power source when plugged into a port configured toreceive both power and data at the device, the method comprising:ascertaining if the external power source is plugged into the port ofthe device, and either: (i) providing power to the circuit from thebattery when the external power source is not plugged into the device;(ii) providing power from the external power source to the circuit andthe battery used to at least recharge the battery when the externalpower source is plugged into the device and when the output of thebattery is below a supply voltage by more than a threshold; or (iii)providing power from the external power source only to the circuit whenthe external power source is plugged into the device and the output ofthe battery is within the threshold of the supply voltage.
 14. Themethod of claim 13, further comprising converting an external powersource voltage to the supply voltage within the device, wherein thesupply voltage is one of the following: approximately 1.8 volts,approximately 3.3 volts, approximately 5.0 volts; or 5.0 volts or less.15. The method of claim 14, wherein providing the external power to thecircuit in the device and the battery to recharge the battery furthercomprises generating a charge current to charge the battery when anoutput voltage of the battery is below the supply voltage by more thanthe threshold.
 16. The method of claim 15, further comprising comparingthe battery voltage output to the supply voltage and either: (i)generating a first signal if the battery voltage output is within thethreshold from the supply voltage, the first signal causing power fromthe external power supply to be provided only to the circuit when theexternal power is received through the port; or (ii) generating a secondsignal if the battery voltage output is below the threshold of thesupply voltage, the second signal causing a charge current to beprovided to the battery to charge the battery when the external power isreceived through the port.
 17. The method of claim 15, furthercomprising disconnecting the external power supply voltage from thebattery after the battery is charged.
 18. The method of claim 15,further comprising switching between (i), (ii) and (iii) such that powerprovided to the circuit from either the battery or the external powersource voltage is substantial without interruption.
 19. The method ofclaim 15, further comprising transmitting and/or receiving data throughthe port of the device.
 20. A battery powered device comprising: arechargeable battery; a serial port that interfaces with a serial buscable for transmitting data to or from the device that includes aplurality of data pins and at least a power pin; a voltage sensor thatsenses a voltage on the power pin; and a battery charging circuit thatdraws a charging current through the power pin of the serial port tocharge the battery when the battery is substantially uncharged.
 21. Thebattery powered device of claim 20, wherein the device comprises apersonal digital assistant.
 22. The battery powered device of claim 20,wherein the device comprises a personal MP3 player.
 23. The batterypowered device of claim 20, wherein the rechargeable battery comprises alithium ion cell.
 24. The battery powered device of claim 20, whereinthe rechargeable battery operates within a voltage range of 3.7 volts to4.2 volts.
 25. The battery powered device of claim 20, wherein theserial port interfaces with a serial bus cable that transmits data to orfrom the device at a rate of at least 100 megabits per second.
 26. Thebattery powered device of claim 20, wherein the serial port interfaceswith a serial bus cable transmits data to or from the device in anasynchronous or isochronous mode.
 27. The battery powered device ofclaim 20, wherein the serial port interfaces with an IEEE 1394 compliantserial bus cable.
 28. The battery powered device of claim 20, whereinthe battery charging circuit operates in a constant current mode. 29.The battery powered device of claim 20, wherein the battery chargingcircuit shuts off when its supply voltage is less than 4.2 volts. 30.The battery powered device of claim 20, wherein the battery chargingcircuit electrically isolates the battery if the battery is fullycharged.
 31. The battery powered device of claim 20, wherein thecharging current is 750 mA.
 32. The battery powered device of claim 20,wherein the voltage sensor and the battery charging circuit are coupledto the serial port via a main bus.
 33. The battery powered device ofclaim 20, further comprising an inrush current limiter configured tolimit an inrush current that flows into the battery powered device whena serial bus cable is inserted into the serial port.
 34. The batterypowered device of claim 20, further comprising a voltage converterconfigured to convert an external voltage received at the power pins ofthe serial port to an internal supply voltage within the range of 1.8volts to 5 volts.
 35. The battery powered device of claim 20, furthercomprising an active circuit operating at a supply voltage within therange of 1.8 volts to 5 volts.
 36. The battery powered device of claim20, further comprising a comparator coupled to the voltage sensor andconfigured to generate a switching signal based upon the sensed voltage.37. The battery powered device of claim 20, further comprising aswitchover circuit configured to supply power to an active circuit viathe battery or a supply voltage received via the power pins of theserial port.
 38. A method for charging a battery of a peripheral device,comprising: inserting a serial bus cable into a serial port of theperipheral device, the serial port comprising a power pin and aplurality of data pins through which data can be transmitted to or fromthe peripheral device; sensing that the voltage at the power pin of theserial port is above a selected threshold; and drawing a charge currentthrough the power pin of the serial port to charge the battery of theperipheral device.
 39. The method of claim 38, wherein the peripheraldevice comprises a personal digital assistant.
 40. The method of claim38, wherein the peripheral device comprises a personal MP3 player. 41.The method of claim 38, wherein the battery operates within a voltagerange of 3.7 volts to 4.2 volts.
 42. The method of claim 38, wherein thebattery is considered to be uncharged when its voltage drops below 3.45volts.
 43. The method of claim 38, wherein the serial port interfaceswith a serial bus cable that transmits data to or from the device in anasynchronous or isochronous mode.
 44. The method of claim 38, whereinthe serial port interfaces with an IEEE 1394 serial bus cable.
 45. Themethod of claim 38, wherein the charge current is 750 mA.
 46. The methodof claim 38, further comprising electrically isolating the battery ifthe battery is substantially fully charged.
 47. The method of claim 38,further comprising suppressing a power surge caused by the insertion ofthe serial bus cable into the serial port.
 48. The method of claim 38,further comprising converting an external voltage received at the powerpins of the serial port to an internal supply voltage within the rangeof 1.8 volts to 5 volts.
 49. A system comprising: a battery powereddevice having a rechargeable battery and a battery charging circuit; anda serial bus cable coupled to the battery powered device, the serial buscable comprising a power transmission line and a plurality of datatransmission lines, wherein the serial bus cable can transmit data to orfrom the battery powered device over the data transmission lines; andwherein the battery charging circuit of the battery powered device drawsa charging current through the power transmission line of the serial buscable if the rechargeable battery is not fully charged.
 50. The systemof claim 49, wherein the battery powered device comprises a personaldigital assistant.
 51. The system of claim 49, wherein the batterypowered device comprises a personal MP3 player.
 52. The system of claim49, wherein the rechargeable battery operates within a voltage range of3.7 volts to 4.2 volts.
 53. The system of claim 49, wherein the serialbus cable transmits data to or from the battery powered device at a rateof at least 100 megabits per second.
 54. The system of claim 49, whereinthe serial bus cable transmits data to or from the battery powereddevice in an asynchronous or isochronous mode.
 55. The system of claim54, wherein the serial bus cable comprises an IEEE 1394 compliant serialbus cable.
 56. The system of claim 49, wherein the battery powereddevice electrically isolates the rechargeable battery when the batteryis fully charged.
 57. The system of claim 49, wherein the chargingcurrent is 750 mA.
 58. The system of claim 49, wherein the batterypowered device comprises an active circuit operating at a supply voltagewithin the range of 1.8 volts to 5 volts.
 59. The system of claim 49,wherein the data transmission lines are separately-shielded twistedtransmission type data lines.
 60. A method for managing power deliveredto a battery-operated peripheral device by way of a cable that includesa number of lines at least one of which is a power line arranged tocarry electrical power from an electrical supply to the device, themethod comprising: detecting a status for the device, wherein the statusis based on whether a first condition relating to a battery in thedevice has occurred and whether a second condition relating toconnection of the cable to the electrical supply has occurred; drawingelectrical power from the electrical supply at a first current if thedevice has a first status; and drawing electrical power from theelectrical supply at a second current level if the device has a secondstatus.
 61. The method of claim 60, wherein the second condition is theattachment of the cable to another device.
 62. The method of claim 60,wherein the second condition is the connection of the cable to anotherdevice such that a data transfer request is received by thebattery-operated peripheral device.
 63. The method of claim 60, furthercomprising converting the electrical power from an external voltage to asupply voltage by a voltage converter unit.
 64. The method of claim 60,wherein the first condition is when a battery in the device is fullycharged.
 65. The method of claim 64, further comprising, if the batteryis fully charged, providing the battery with electrical power from theelectrical supply at a third current level.
 66. The method of claim 65,wherein the third current level is essentially zero amps.
 67. The methodof claim 65, wherein the cable includes two twisted pairs of wirescarrying data.
 68. The method of claim 67, wherein the two twisted pairsof wires are separately shielded.
 69. The method of claim 68, whereinthe cable is an I.E.E.E. 1394 compliant cable.
 70. A portable consumerelectronic product comprising: a sensor unit arranged to detect a statusfor the device, wherein the status is based on whether a first conditionrelating to a battery in the device has occurred and whether a secondcondition relating to connection of the cable to the electrical supplyhas occurred; a switchover circuit arranged to draw electrical powerfrom the electrical supply at a first current if the device has a firststatus, and to draw electrical power from the electrical supply at asecond current level if the device has a second status.
 71. The portableconsumer electronic product of claim 70, further comprising a voltageconverter unit arranged to convert the electrical power from an externalvoltage to a supply voltage.
 72. The portable consumer electronicproduct of claim 70, wherein the switchover circuit is further arrangedto, if the battery is fully charged, provide the battery with electricalpower from the electrical supply at a third current level.
 73. Theportable consumer electronic product of claim 70, wherein the thirdcurrent level is essentially zero amps.
 74. The portable consumerelectronic product of claim 70, wherein the cable includes two twistedpairs of wires carrying data.
 75. The portable consumer electronicproduct of claim 74, wherein the two twisted pairs of wires areseparately shielded.
 76. The portable consumer electronic product ofclaim 75, wherein the cable is an I.E.E.E. 1394 compliant cable.